An assessment of the effects of discontinuities and a gaseous environment on the low-cycle fatigue behavior of NiMoV generator rotor forging steel is presented. Discontinuities were positioned near the notch root in blunt-notch compact tension specimens machined from trepanned core bars. These specimens were subjected to cyclic loading with two maximum stress/yield stress ratios, 0.95 and 1.37. For tests conducted in air, discontinuities reduced the average crack initiation and propagation cycles by factors of as much as 6 and 1.5, respectively. The discontinuity influence was greater at the low cyclic load. Hydrogen reduced the cycles for crack propagation in discontinuity-free specimens by as much as a factor of 2 but had less influence on initiation. In specimens containing discontinuities, the crack propagation interval was shorter in hydrogen than in air, thus indicating the existence of a discontinuity-environment interaction. The variability in cycles to crack initiation from specimen to specimen was reduced by taking into account the initiation criterion as well as the discontinuity size and location with respect to the notch. The relation between discontinuities, cracks, and the service performance of generator rotors is discussed.
With G. A. Miller, T-T. Shih, and C. E. Swenson, "Effect of Discontinuities on Low-Cycle Fatigue Behavior of NiMoV Rotor Forging Steel," in Low-Cycle Fatigue and Life Prediction, STP 770, C. Amzallag, B. N. Leis, and P. Rabbe, Eds., American Society for Testing and Materials, Philadelphia, Pa., 1982, pp 227-253.